Work in this laboratory will employ a variety of anatomical (intracellular markers) and physiological (intracellular recording) methods in continuing to examine the relationships among primary afferents, identified mechanosensory interneurons (MSI), and the lateral giant, all of which participate in the crayfish escape response. In particular, we will examine: 1) the morphology of different functional classes of primary afferents within the mechanosensory system; 2) the topographic relation of mechanosensory afferents (MSA) to other proprioceptive and exteroceptive classes of primary sensory cells in the central neuropile; 3) the comparative morphology of MSIs occupying different levels of the connectivity hierarchy; and 4) the topographic segregation of terminals from identified MSIs on the dendritic tree of the lateral giant. Further studies of the mechanism of presynaptic inhibition exerted on MSAs will be conducted using sucrose gap and intracellular recording. The central questions to be pursued are the ionic dependence of primary afferent depolarization, the nature of the neural elements which constitute the inhibitory circuit, and the distribution of both pre- and postsynaptic inhibition, by this circuit, to various elements within the mechanosensory system. Experiments using the muscle receptor organ afferents will examine the mechanism and time course of the change in membrane voltage responsd to GABA iontophoresis we have found following axotomy. Finally, studies of the tonic abdominal neuromusclular system will attempt to reveal the basic integrative organization of a newly discovered light-modulated postural adjustment reflex.